Combined oscillator and folded slot antenna for fuze useful in small projectiles



July 23. 1968 s. MAKRANCY 3,394,373

COMBINED OSCILLATOR AND FOLDED SLOT ANTENNA FOR FUZE USEFUL IN SMALL PROJECTILES iled April 26, 1967 2 Sheets-Sheet 1 V I2 IO :F

o AMPLIFIER S b T OCQR ---n l3 FIRING CIRCUIT J: DETONATO R AMPLIFIER o +V INVENTOR.

STEPHEN L. MAKRANCY ATTORNEY.

July 23, 1968 s, L. MAKRANCY 3,394,373

COMBINED OSCILLATOR AND FOLDED SLOT ANTENNA FOR FUZE USEFUL IN SMALL PROJECTILES Filed April 26, 1967 2 Sheets-Sheet 2 9- INVENTOR.

we STEPHEN 1.. MAKRANCY 29 BY ATTORNEY.

United States Patent 3 394,373 COMBINED OSCILLATOR AND FOLDED SLOT ANTENNA FOR FUZE USEFUL IN SMALL PROJECTILES Stephen L. Makrancy, Cincinnati, Ohio, assignor to Avco Corporation, Richmond, Ind., a corporation of Delaware Filed Apr. 26, 1967, Ser. No. 633,748 8 Claims. (Cl. 3438) ABSTRACT OF THE DISCLOSURE This is a combined oscillator-radiator device comprising a folded slot antenna including as an integral part a resonator line within the slot, and an active element or transistor. The slot is the radiator, the line is the tank circuit, and the transistor completes the generator of oscillations. The device is of particular utility in proximity fuzes.

Field of the invention The principal object of the invention is to provide a combined oscillator-radiator device of the type indicated in the above abstract.

The present invention relates to circuits for generating and radiating radio frequency energy and more particularly to a novel combination of a folded slot antenna including a frequency determining element or tank circuit and an active element which, taken together with that tank circuit, comprises an oscillator. The folded slot antenna includes a resonant line which is the frequency determining element or tank circuit of the oscillator. The structure is compact and contains no bulky components such as cavity resonators or other tuned circuits, separate matching networks, and transmission lines.

The present device utilizes a length of line near one half electrical wavelength long, as the frequency determining element. The resonant line is also an integral part of a folded slot antenna as well as the tank circuit of the oscillator. Since one is an integral part of the other, separate transmission lines, separate tuned circuits and matching networks, along with their associated losses, Weight and cost, are eliminated.

The generation of a VHF or UHF radio frequency is usually accomplished in proximity fuze devices by means of an oscillator utilizing a separate cavity resonator or some other form of tuned circuit as the frequency determining element. Conventional cavities and the like are costly to fabricate and bulky. In devices where the radiating antenna is separate from the signal source (oscillator-resonator) impedance matching devices may be necessary at the input and output of the radio frequency transmission line. Matching networks are to be avoided, if possible, due to their added cost and weight; and also, on account of the radio frequency power losses in the several networks during transmission and reception.

Conventionally used prior art fuze devices are characterized by significant disadvantages. Since the antenna is conventionally separate from the oscillator, one impedance matching network is needed for coupling the oscillator to a waveguide or coaxial transmission line and another network is needed to couple the line to the antenna. These networks attenuate the signal transmitted from the antenna and also the signal coupled back to the oscillator to produce the Doppler effect. The networks also add to the bulk and weight of the fuze as well as to its cost.

In the prior art is the Kuecken patent No. 3,296,616, applied for on June 1, 1965, issued by the United States Patent Office on Jan. 3, 1967. That device represents a long step forward in the art but it does not eliminate a cavity resonator.

For a better understanding of the invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following description of the appended drawings.

Description of the drawings In the drawings, FIG. 1 is a block diagram of a Doppler fuzing system incorporating an oscillator-detector in accordance with the invention, i.e., a system in which the invention is of particular utility;

FIG. 2 is a fragmentary plan view, in section, showing a folded slot antenna of the resonant line;

FIG. 3 is a fragmentary plan view, in section, showing the slot antenna, resonant line and associated elements involved in making up an oscillator radiator in accordance with the invention;

FIG. 4 is a perspective view of a particular embodiment of the invention as incorporated in a practical structure, showing the parts in exploded condition;

FIG. 5 is an edge View of the main body portions of the FIG. 4 embodiment; and

FIG. 6 is a fragmentary perspective view showing the dielectric housing ring and the resonant line and folded slot antenna of the FIG. 4 embodiment.

Detailed description of the invention In a system shown in the block diagram of FIG. 1, an RF. (i.e. radio frequency) oscillator-detector 10 energizes an antenna 11 which propagates the R.F. energy toward a target (not shown). Upon reaching the target, a fraction of this energy is reflected back to the antenna and subsequently conducted to the oscillator-detector where it combines or mixes with the transmitter frequency, f When the transmitting-receiving system and the target are both stationary, the Doppler frequency, f is 0 since f =2V,-f where V is the relative velocity of the target in relation to the transmitter receiver and is the velocity of light. When the transmitting-receiving system is receding from the target, the received signal frequency is f f on the other hand, when approaching the target, the received signal frequency is f +f When the transmitted frequency t is heterodyned with the received signal frequency f if a Doppler frequency f results which, if within the range of expected Doppler frequencies as determined by the frequency-response characteristic of an amplifier 12, will activate the remaining circuitry consisting of a firing circuit 13 and a detonator 14, as established by the state of the art. Since isolation between the transmitted and received signals is achieved as a result of the frequency separation due to the Doppler effect, a single antenna may be used for both transmission and reception.

The units 10 and 11 of FIG. 1 are included in a combined oscillator-radiating unit in accordance with the invention.

Referring now specifically to FIG. 2 there is shown a plane configuration of a folded slot antenna. It consists of a slot 16, cut into a conducting ground plane 17. Within the slot is placed a fiat conducting strip 18, mechanically supported by any suitable nonconducting dielectric material. Maximum slot impedance occurs at the center of this configuration at points 0, c, one at the edge of the conducting strip 18 and the other at the edge of the ground plane 17. At these connection points the slot impedance is approximately one fourth that of a conventional slot.

Slot folding reduces antenna impedance and facilitates matching the antenna to the fuze oscillator. Employed as part of the oscillator tank circuit, the folded slot offers considerable flexibility in feedback control as well as relieving the critical positioning requirements encountered when a low source impedance transistor circuit is combined with a conventional high impedance slot antenna.

FIG. 3 shows a combined slot antenna, transmission line and active element, the latter to make up an oscillator, in accordance with the invention. The active element here shown is a solid state device r transistor 19 having its base 20 connected to point a and its collector connected to the ground plane near point b. The FIG. 3 configuration is a type of Colpitts oscillator with the transistor base connected to a feed point. A ca acitor 21 is connected between the collector and the emitter elements in order that the circuit may provide the feedback requisite for oscillation. Connected between one end of the transmission line 18 and the ground plane is a resistor 22 which establishes the transistor bias level. Optionally connected between the other end of the line 18 and the ground plane 17 is a capacitor 23. The system of FIG. 3 operates continuously when the capacitor 23 is disconnected and as a relaxation oscillator when the capacitor 23 is in circuit, the rate of relaxation being dependent on the value of capacitor 23. In series circuit between the emitter of transistor 19 and the negative terminal of the source of bias currents (not shown) is a combination of inductance 24, one element of a feed through capacitor 27 and a resistor 26. Capacitor 27, of coaxial construction, comprises, effectively, two plates, of which one is ungrounded and another is connected to ground whereby the inductor 24 and the capacitor 25 function as a radio frequency filter and permit only the Doppler signal voltages, developed across resistance 26, to be fed to the Doppler amplifier. It will be understood that the terminal resistor 26 provides an output to a Doppler amplifier such as that indicated by the reference numeral 12 in FIG. 1.

A specific embodiment of the invention is shown in FIGS. 4 and 5. The principal housing or frame member is a ring 9 which is copper clad on the top and bottom as is shown at 28 and 29, the copper claddings comprising the ground plane or folded slot antenna 17. This structure is equivalent to the resultant if the FIG. 2 ground plane were arranged in circular configuration. Disposed between the abutting edges of the ends of the folded slot antenna is a shorting bar '8. The shorting bar 8 is the equivalent of the two vertical portions of ground plane metal adjacent the ends of a slot in FIG. 2. The flat center conducting strip or resonant line 18 is held in place by a groove in the ring 9 of nonconductive dielectric material. The copper 28, 29 on both fiat sides provides good electrical contact to two conducting hemispheres 30, 31. The ends of the flat conducting strip or line 18 are fastened in a manner that insures insulation from the ground plane 17 and established by the copper clad.

The oscillator circuit components, including the transistor 19, resistor 22, choke 24, and capacitors 21 and 23 occupy space in the dielectric material between the two copper clad surfaces.

A structure of adequate size in the center of the ring configuration provides housing for the power supply, Doppler amplifier 12 and firing circuit (not shown). When the major components in the exploded view of FIG. 4 are assembled, the ring is in electrical contact with the two hemispheres 30 and 31 through the shorting bar. The shorting bar 8 provides electrical contact between the two hemispheres. The hemispheres do not function as resonators but they aid in establishing an effective ground plane. The shorting bar 8 serves as a direct current connection to the amplifier.

The oscillator circuit employed in the circular configuration of the folded slot antenna is the same as that of FIG. 1, which is a Colpitts circuit. However, other conventional oscillator circuits may be used with an oscillator device that is either a transistor or a vacuum tube.

The above antenna-oscillator configuration forms a compact structure with a minimal number of components. It contains no costly and bulky separate resonators since the fiat conductive strip 18, which is an integral part of the antenna and oscillator tank circuit, is the frequency determining element. This same integral relationship eliminates the need of a transmission line and separate matching networks.

While the spheres 30 and 31 may carry current the ring structure comprising the elements 28 and 29 (making up 17), 9, 19 and associated elements functions as an oscillator-radiator, even when disassociated from the conductive hemisphere elements 30 and 31.

While there has been shown and described what is considered to be the preferred embodiment of the invention, various changes and modifications may be made without departing from the true scope of the invention, as claimed in the appended claims.

I claim:

1. A combined oscillator-antenna structure comprising:

planar conductive means formed with a slot,

a central line within the slot and cooperating with the conductive means to provide a folded slot antenna, and

means including an active element coupled between said central line and said conductive means to complete a generator of oscillations radiated by said antenna, the frequency of said oscillations being determined by said line as a resonant element.

2. An oscillator-antenna structure in accordance with claim 1 in which the active element is a transistor having base and collector and emitter electrodes, the base being connected to said line and the collector being connected to said planar conductive means.

3. An oscillator-antenna structure in accordance with claim 2 including a feedback capacitor coupled between the emitter and collector of said transistor.

4. An oscillator-antenna structure in accordance with claim 3, a source of bias for said base, and a bias level resistor connected between one end of said line and the planar conductive means, said source and said planar conductive means and said line and said base and emitter defining a path for bias current.

5. An oscillator antenna structure in accordance with claim 4, as incorporated in a Doppler radar receiving system, including a Doppler amplifier, and a filter intercoupling the emitter of said transistor and the Doppler amplifier, said emitter being proportioned to pass Doppler frequencies.

6. An oscillator-antenna structure in accordance with claim 5 and a second capacitor connected between the other end of said line and the planar conductive means whereby the oscillations are relaxation oscillations.

7. A combined oscillator-antenna structure comprising a dielectric ring,

a ground plane made up of conductive coatings on both sides of said ring, defining a slot,

a central line imbedded in the ring and within the slot provided by said ground plane and cooperating with the ground plane to provide a folded slot antenna, and

means including a transistor coupled between said central line and said ground plane to complete a generator of oscillations radiated by said antenna, the

5 6 frequency of said oscillations being determined by References Cited said line as a resonant element. UNITED STATES PATENTS 8. A comblned oscillator-antenna structure comprising; 2,751,589 6/1956 Cary 343767 planar conductive means formed with a slot, at central 5 330741063 1/1963 Horton 1O2 70-2 line positioned within the slot to cooperate with the 3296616 1/1967 Kuecken conductive means to provide a folded slot antenna, OTH REF and means connected to the planar conductive means and connected to and utilizing a conductive path through 10 RICHARD FARLEY Primary Examiner said central line to complete a generator of oscillations radiated by Said antenna C. L. WHITHAM, Asststam EXIIITIl/ZEI'.

Wireless World, August 1964, pp. 400, 401. 

